The objective of evolved universal terrestrial radio access (E-UTRA) and long term evolution (LTE) in wireless communications is to develop a radio access network towards a high-data-rate, low-latency, packet-optimized system with improved system capacity and coverage. In order to achieve these goals, an evolution of the radio interface as well as the radio network architecture is being considered. For example, orthogonal frequency division multiple access (OFDMA) and frequency division multiple access (FDMA) are proposed air interface technologies to be used in the downlink and uplink transmissions, respectively, instead of using code division multiple access (CDMA), which is currently used in 3rd Generation Partnership Project (3GPP) communication systems. Another change includes applying all packet switched service, which means all the voice calls will be made on the packet switched basis.
Packet switched communications operate on a random access channel. The physical channel specification for LTE specifies that the random access burst occupies a bandwidth corresponding to 72 sub-carriers (6 resource blocks). The set of six resource blocks is referred to as one time-frequency random access resource, or alternatively, resources of one LTE physical random access channel (PRACH). For the system flexibility, having a configurable number of time-frequency random access resources in one radio frame (10 ms) depends on the system bandwidth and the random access load. The existence of any additionally configured time-frequency random access resources needs to be explicitly signaled to wireless transmit/receive units (WTRUs).
There may be multiple random access preambles that are available for the access in one time-frequency random access resource, and the number of random accesses that expect the responses in a certain time window may vary greatly. If an evolved Node-B (eNB) always needs to signal all responses in one transport block per one random access-radio network temporary identity (RA-RNTI), the resultant size of the transport block may reduce the scheduling flexibility of the random access response.